md/raid10: fix still_degraded being inverted in raid10_sync_request()

Commit fe6a19d40c ("md/md-bitmap: merge md_bitmap_start_sync() into
bitmap_operations") converted still_degraded from int to bool, but
inverted the assignment in the loop that checks whether the array will
still be degraded after the current device is recovered:
"still_degraded = 1" became "still_degraded = false".

As a result, recovering a device while another mirror is still missing
calls md_bitmap_start_sync() with degraded == false, which clears bitmap
bits that the still-missing device needs.  When that device is re-added,
its bitmap-based recovery finds the bits already cleared and skips every
region written while the array was degraded, so it is marked In_sync
while holding stale data: silent corruption.

Reproducer (raid10 near=2, 4 disks, internal bitmap):
 - fail and remove one disk of each mirror pair
 - write to the degraded array
 - re-add both disks and let recovery finish
 - "check" reports mismatch_cnt=262272 after 256 MiB of degraded
   writes and file contents differ; the second disk's "recovery"
   completes in milliseconds because everything is skipped

The same conversion in raid1 got it right (still_degraded = true).
Restore the correct value.

Fixes: fe6a19d40c ("md/md-bitmap: merge md_bitmap_start_sync() into bitmap_operations")
Cc: stable@vger.kernel.org
Signed-off-by: Yunye Zhao <yunye.zhao@linux.alibaba.com>
Reviewed-by: Mykola Marzhan <mykola@meshstor.io>
Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>
Reviewed-by: Yu Kuai <yukuai@fygo.io>
Link: https://patch.msgid.link/20260723135535.101995-2-yunye.zhao@linux.alibaba.com
Signed-off-by: Yu Kuai <yukuai@fygo.io>

drivers/md/raid10.c

@@ -3337,7 +3337,7 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
 				struct md_rdev *rdev = conf->mirrors[j].rdev;
 
 				if (rdev == NULL || test_bit(Faulty, &rdev->flags)) {
-					still_degraded = false;
+					still_degraded = true;
 					break;
 				}
 			}